Silencing device



Feb. 14, 1939. L. N 7 2,147,311 I SILENCING DEVICE Filed Oct. 8, 1937 INVENTOR RICHARD L. NASH ATTORNEY Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE SILENCING DEVICE Application October 8, 1937, Serial No. 167,995

3 Claims.

This invention relates to means for minimizing sounds created by pulsations set up in a fluid by operation of a machine, and more particularly to a silencing device adapted to reduce sound produced in the intake passage or the discharge passage of a fluid compressor.

The principal object of the invention is to provide a silencing device of simple and compact construction adapted to be interposed in the conduit between a fluid compressor and a receiving reservoir for absorbing or breaking sound waves resulting from the pulsating operation of the compressor, which sound waves might otherwise be transmitted to the reservoir and amplifled.

Another object of the invention is to provide a silencing device of the above type having a chamber with sound reflecting surfaces so formed as to effect the breaking up and scattered distribution of sound waves entering from the compressor, for thereby reducing the noise of operation.

Other objects and advantages of the invention will appear in the following more detailed description thereof taken in connection with the accompanying drawing, wherein:

Fig. 1 is a sectional view of a silencing device constructed in accordance with my invention; and

Fig. 2 is a sectional View taken on the line 2-2 of Fig. 1.

Referring to the drawing, the silencing device comprises a casing 3 having a circular central chamber 4 communicating with an inlet passageway 5 which is formed in a portion 6 of the casing, and an annular chamber 7 formed in the casing surrounding the central chamber and communicating with an outlet passageway la, which is disposed perpendicularly to the axes of said chambers. An annular opening or slot 9 is formed in the casing for connecting the chambers 4 and l. The passageway 5 is preferably connected to a fluid pressure conduit or chamber which is the source of the sound wave, such as the fluid discharge portion of a compressor, not shown, by means of a pipe 8 having screw threaded engagement with the casing 3, and the passageway la may likewise be connected to a pipe 10 leading to a receiving reservoir, not shown. It will be apparent that fluid under pressure supplied to the pipe 8 will be free to flow through the passageway 5, the chamber 4, the annular slot 9, the annular chamber 1, the passageway la and the pipe ID to the receiving reservolr.

According to my invention, a paraboloidal refiecting surface II is provided as one wall of the chamber 4, and is disposed opposite the portion 5 of the casing and coaxially with the inlet passageway 5. The portion 5 of the casing projects into the chamber 4 and has formed thereon an annular rib !2 which forms the mouth of the inlet passageway 5. It has been found that the rib [2 may be so disposed with respect to the focal point of the paraboloidal surface ll that 10 the crest of a sound wave advancing into the chamber 4 from the passageway 5 will escape the confinement of the passageway and spread or diverge in various directions as if traveling from the focal point as the apparent center.

Also formed on the portion 6 of the casing are several fiat annular reflecting surfaces such as l4, l5 and I6, which are disposed in step-like formation surrounding the passageway 5, the several annular surfaces being set back different distances from the rib I 2. It will be noted that a wall I! is formed across the annular chamber 1 at one side of the outlet passageway la.

According to accepted theories as to the behavior of sound and other waves, the operation of the silencing device is as follows:

Let it be assumed that sound waves are traveling downwardly through the pipe 8 and the passageway 5, as viewed in Fig. 1 of the drawing, each advancing wave front as it emerges from the passageway spreading outwardly into the chamber 4 in various directions, as if radiating from the focal point of the paraboloidal surface H, by reason of the relative location of the rib l2 and said focal point as already de scribed. It will be understood that waves impinging on said surface from the focal point will be reflected in paths parallel to its axis. Considering one of the sound waves as spreading outwardly from the focal point against the paraboloidal surface H, it will be apparent that the portion of the wave striking the surface directly beneath the passageway 5 is reflected back into the passageway, while other portions of the sound wave which are reflected from the outer area of the surface H impinge against the fiat surfaces l4, l5 and I6, and thence return to the paraboloidal surface and back through the focal point by different paths. The sound wave is thus broken up in the chamber 4 into portions which 5 are reflected over paths of various lengths and for indefinite periods of time, so that the crest of the sound wave is largely distributed or stretched out indefinitely.

It is possible that some of the sound waves passing through the chamber 4 will travel therefrom through the annular slot into the chamber 1, it being probable that the crest of such a wave would pass all parts of the slot 9 simultaneously, due to the circular symmetry of the chamber 4. Assuming that such is the case, the entire wave crest does not appear at the outlet passageway la at once, but is instead drawn'out because the various portions of the waves are at difierent distances from the outlet passageway. The wall I? is effective at this time to prevent the portions of the sound wave from traveling toward the outlet passageway from both directions around the annular chamber 1. Thus the chamber 1 is adapted to effect further breaking up and redistribution of any sound wave entering from the first chamber 4, so that objectionable noise of operation of a compressor or the like is substantially prevented from being transmitted from the inlet pipe 8 to the outlet pipe it leading to the receiving reservoir.

While one illustrative embodiment of the invention has been described in detail, it is not my intention to limit its scope to that embodiment or otherwise than by the terms of the appended claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

l. A silencing device adapted to check the advance of sound waves through a fluid conduit connected to a fluid compressor or the like, comprising a casing having an inlet passageway through which fluid in the conduit flows, a circular chamber formed concentrically with said passageway and communicating therewith, one wall of said chamber comprising a paraboloidal reflecting surface positioned coaxially with and opposite to said passageway, the focus of said surface being so spaced from the mouth of said inlet passageway as substantially to coincide with the apparent center of divergence of sound waves issuing therefrom, and the opposite wall projecting into said chamber and comprising a plurality of fiat reflecting surfaces surrounding said passageway and variously spaced from the paraboloidal surface, and an annular chamber concentrically surrounding said circular chamber and communicating therewith, said annular chamber having therein a baflle wall and an outlet passageway formed adjacent said wall.

2. A silencing device adapted to be interposed in the fluid discharge conduit of a fluid compressor to dissipate sound Waves produced by operation of said compressor, comprising a casing having an inlet passageway, a circular chamber formed concentrically of and communicating with said inlet passageway, the wall of said chamber opposite said passageway constituting a paraboloidal reflecting surface so positioned that its focus approximately coincides with the apparent center of divergence of sound waves issuing from said passageway, the opposite wall of said chamber constituting a series of fiat annular reflecting surfaces arranged in steps surrounding and receding from the mouth of said passageway, and an outlet passageway communicating with said chamber and disposed at an angle to the axis of said inlet passageway and said chamber.

3. A silencing device adapted to be interposed in the fluid discharge conduit of a fluid compressor to dissipate sound waves produced by operation of said compressor, comprising a casing having an inlet passageway, a circular chamber formed concentrically of and communicating with said inlet passageway, the wall of said chamber opposite said passageway constituting a paraboloidal reflecting surface so positioned that its focus approximately coincides with the apparent center of divergence of sound waves issuing from said passageway, the opposite wall of said chamber constituting a series of flat annular reflecting surfaces arranged in steps surrounding and receding from the mouth of said passageway, an arcuate chamber formed conceniii 

